In prior art document U.S. Pat. No. 6,154,546 it is known to apply a tube connected to one of the microphones in a directional digital hearing aid with more than one microphone. According to the patent the probe tube is adapted to be fitted inside the ear of the patient and to convey sound signals there from to one of the microphones of the hearing aid. When this system is used, two microphones are necessary as one microphone is to sense the conditions in front of the tympanic membrane while the other microphone at the same time will record the sound level at the ear.
From U.S. Pat. No. 6,118,877 it is further known to make use of a tone generator in the hearing aid to produce audio sounds for testing purposes.
With the prior art hearing aids and methods it is not possible to make real ear measurements with only one microphone.
Other known ways of making real ear measurements involve the use of further microphone modules and tubes and further electric leads connecting the microphone modules with the fitting unit. This is not much liked by hearing aid dispensers. Thus many hearing aids are dispensed without real ear measurements, and the values used in the fitting procedure are not verified. The invention seeks to solve this problem by providing a real ear measurement solution which does not require more electric wires or other components which the dispenser needs to operate. Further it is the object of the invention to provide a measurement method which can be performed with hearing aids with only one microphone and wherein the measurement is performed with the hearing aid instrument itself, such that more precise and reliable data are gained.